Perhaps no disease known to modern civilization is viewed with as much general fear as cancer. Heart attacks and strokes tend to be thought of as natural hazards of age, and either a normal end to a satisfactorily long life or, when they occur in middle-age, the wages of a sedentary lifestyle. In contrast, cancer is thought of as an unpredictable disease that strikes indiscriminately at rich and poor, fat and thin, old and young, as if it owed nothing to external causes. J. Cairns, Mutation, Selection and Cancer, Nature, Vol. 255, pp. 197-200 (1975).
Each year in the United States, approximately 600,000 new cases of cancer are diagnosed; and one out of every five people in this country will die from cancer, or from complications associated with its treatment. However, most of these cancer patients are not killed by their primary tumor. They succumb instead to metastasis: multiple, widespread tumor colonies established by malignant cells that detach themselves from the original tumor and travel through the body, often to distant sites. G. Nicholson, Experimental Tumor Metastasis: Characteristics in Organ Specificity, Bioscience, Vol. 28, No. 7, pp. 441-47 (July, 1978). If a primary tumor is detected early enough, it can usually be eliminated by surgery, radiation, chemotherapy or photodynamic therapy, or some combination of these treatments. Unfortunately, the metastatic colonies are harder to detect and eliminate because they often are not visible to the unaided eye, being microscopic in size or hidden within tissues or organs. This difficulty in detecting and eradicating metastasis enhances cancer's image as a fleeting and unpredictable disease.
Presently, primary tumor detection is accomplished by x-ray, ultrasonography, nuclear magnetic resonance (NMR), positron emission tomography (PET), chemical laboratory analysis and biopsy. However, metastatic dissemination from the primary tumor often is impossible to detect with these methods. As a result, there is a definite need for an accurate and sensitive technique to detect and sample these elusive metastatic colonies.
Every diagnosis of cancer must be documented by a definitive biopsy. In addition, biopsy is a crucial technique in the management of cancer. Since different types of neoplasms have their own responses to the various modalities of therapy, a histological diagnosis is imperative in planning the appropriate management of malignant disease. Moreover, biopsy provides the pathologist with adequate samples of tumor. In addition to the biopsy, an immediate frozen section during intraoperative procedures is often necessary for final diagnosis of malignancy. However, frozen section histology is both time consuming and expensive. Performed during the operation, this procedure requires the surgeon to halt the surgery midstream until the pathology of the suspected cancerous tissue is determined. Once determined, the operation can then be resumed. Consequently, the availability of a device that provides an instant indication of metastasis, as well as a simultaneous biopsy sample of the suspected tissue during the operative procedure would satisfy the need for a definitive biopsy and eliminate the disadvantages of frozen tissue histology.
With this in mind, it has been known for more than sixty years that some porphyrins are selectively retained by neoplastic tissue. A. Policard, Etudes Sur Les Aspects Offerts Par De Tumeurs Experimentales Examineesa La Lumiere De Woods, C. R. Seanc Soc. Biol. 91:1423-4 (1924). These same porphyrins also emit a characteristic dual-peaked red fluorescence after being exposed to light containing the appropriate wavelength to excite fluorescence. Although any fluorescent agent selectively retained by cancerous tissue can be used, Lipson in 1961, used these two properties of porphyrins to develop a primary tumor detection system. Lipson also introduced hematoporphyrin derivative (HPD) which demonstrated better tumor-localizing properties. R. L. Lipson, et al., The Use of a Derivative of Hematoporphyrin in Tumor Detection, J. Nat. Cancer Inst. 26:1-11 (1961). Dougherty then took advantage of HPD's photosensitizing properties to eradicate tumors, opening the door to HPD's use as a therapeutic cancer modality. Since that time, HPD's primary importance in the cancer arena has been as a potential cancer treatment, and extensive investigation has been done to refine its use. T. Dougherty, C.R.C. Critical Review in Oncology/Hematology, S. David, E. D. (C.R.C. Press, Florida, 1984).
Termed, "Hematoporphyrin Derivative Photodynamic Therapy," HPD's mechanism in cancer therapy is based on its affinity for malignant tumors relative to other tissues. When injected intravenously, HPD localizes at higher levels in malignant tumor tissues than in normal tissues. The HPD is then activated by light to catalyze the production of singlet oxygen from available triplet oxygen. Although the exact mechanism of necrosis is unclear, it has been suggested that the reactive singlet oxygen oxidizes unsaturated carbon-carbon bonds in amino acids and fatty acids. The ensuing loss of the structural integrity of cellular macromolecules results in cytocidal effects and tumor necrosis. Li, et al., Application of HPD and Laser-Induced Photo Dynamical Reaction in the Treatment of Lung Cancer, Laser in Surgery and Medicine, 4:31-7 (1984).
This use of HPD in photodynamic cancer treatment is a very exiting and rapidly developing possibility. However, a complete cure for cancer is impossible without specific detection and ablation of those cancer cells that have disseminated throughout the organism via the lymphatic or circulatory system. The present invention deals with this problem of metastasis and facilitates a potential cancer cure by utilizing HPD's tumor-seeking properties and fluorescence to instantly detect and simultaneously biopsy cancerous tissue undetected by conventional methods.
Although much of the research involving HPD has been with regard to cancer treatment, several investigators have looked at HPD's tumor detection capabilities. However, the goal of this detection work has been to use surface fluorescence to localize carcinoma in situ which by definition has not penetrated the basement membrane, and thus is not metastasizing. In contrast, the present invention is capable of detecting and biopsying metastatic sites, as well as determining tumor depth and size. In fact, the present invention is based in part on the discovery that metastatic sites which generally are undetected by conventional diagnostic methods produce a fluorescence spectra different from that of primary tumor and normal tissue. The photosensitizer enhanced fluorescence spectra of metastatic sites are consistently and significantly higher than the fluorescence spectra of both the primary tumor and normal tissue.
Profio, et al. described a fluorescence bronchoscopy system for localizing small lung tumors and carcinomas in situ by HPD fluorescence. E. Profio, Fluorescence Bronchoscopy for Localization of Carcinoma In Situ, Med. Phys. 10 (1), pp. 35-39 (Jan./Feb. 1983). Ankerst, Montan and Svanberg each studied HPD laser-induced fluorescence in normal and tumor rat tissue to determine optimal HPD surface fluorescence for tumor detection. J. Ankerst, et al., Laser-Induced Fluorescence Studies of Hematoporphyrin Derivative (HPD) in Normal and Tumor Tissue of Rat, Applied Spectroscopy, Vol. 38, No. 6, pp. 890-96 (1984); S. Montan, Multicolor Imaging and Contrast Enhancement in Cancer-Tumor Localization Using Laser-Induced Fluorescence in Hematoporphyrin-Derivative-Bearing Tissue, Optics Letters, Vol. 10, No. 2, pp. 56-8 (February, 1985); and K. Svanberg, Fluorescence Studies of Hematoporphyrin Derivative in Normal and Malignant Rat Tissue, Cancer Research, 46:3806-808 (August, 1986). Kato, et al. described four different bronchoscopic fluorescence detection systems that have facilitated the localization of HPD-labelled squamous cell carcinoma of the trachea and the central bronchi. H. Kato, et al., Early Detection of Lung Cancer by Means of Hematoporphyrin Derivative Fluorescence and Laser Photoradiation, Clinics in Chest Medicine, Vol. 6, No. 2, pp. 337-53 (June, 1985).
Others have attempted to utilize HPD's tumor seeking properties to detect cancer, but have failed. This failure was apparently due to an intrinsic abundance of free porphyrins in cancerous tissue and HPD's uptake in normal tissue. It therefore was concluded that HPD did not provide a good in vivo technique for detection. The present invention, however, overcomes these failures, and is capable of detecting cancer in situ as well as difficult to find metastasis. Moreover, once detected, the present invention also allows for the immediate biopsy of metastatic sites.
In U.S. Pat. No. 4,930,516 to R. R. Alfano, there is described a method and apparatus for detecting the presence of tumors in situ using the native visible luminescence of the cell. The invention is based exclusively on the intrinsic fluorescence of the cell produced by native flavins and porphyrins found in abundance in subcellular organelles.